On the Internet, users actively access WWW servers from Web browsers to browse document data, image data, and the like. This mechanism is implemented in such a manner that WWW servers used to disclose information on the Internet, and clients used to browse such information, are connected via the Internet, and each client can browse information disclosed by the servers. Each WWW server stores a document which is called a home page that describes information to be disclosed in HTML, and the Web browser on the client side accesses such home page to display it on the client computer. The Web browser on the client side can get required information by tracing links in displayed pages.
Furthermore, as a method of downloading files managed by the server, a File Transfer Protocol (to be abbreviated as FTP hereinafter) is known. This FTP is a mechanism for transferring a file on the server to a client server at a time via a network. As a protocol for fragmentarily accessing and displaying an image file, Flashpix/IIP is known. This IIP is a protocol optimal to the format “Flashpix” of an image data file, and partial access to image data is made for respective tiles specified by Flashpix.
On the other hand, when this IIP is directly applied to JPEG2000, since encoded data of each scalability in JPEG2000 is difference data based on data of scalability one level lower than that scalability, the client must cache received fragmentary encoded data.
However, when the client saves all these fragmentary encoded data, and finally browses the entire image with the highest resolution and highest SNR, all data of a JPEG2000 bitstream on the server are cached on the client side. This may cause the following problems. That is, in the client terminal with a small memory size, the memory overflows during browsing of an image, and an image according to a user's request can no longer be displayed.
Furthermore, since JPEG200 uses differential data, if the memory overflows, and newly received data is overwritten on the already cached data, an image (that the user wants) cannot be accurately displayed.